To start off, what is the purpose in installing shackles? The purpose is the raise the rear end of the vehicle. Depending on how worn your rear leaves are in the back, you will get anywhere from 1" to 1.75" of lift. If you are getting shackles, I recommend Warrior shackles part number WAR153. They are sturdy, and will hold up well.
First off, what you need for the installation. You will need 2 jackstands, a jack, lug wrench, and socket set. You might also want some PB Blaster to soak the bolts with first. First thing, using your rear axle, jack up your truck so your rear tires are at least an inch or 2 off the ground. Then place a jackstand in front of the leaf springs on the frame, on both sides, here:
Now lower the jack enough for the truck to be resting on the jack stands. These need to be set high enough that you can have it fully resting on these, and the wheels off the ground. If you do not have tall enough ones, that is not a problem. In that case, just release the jack holding the axle enough that the frame is resting on the jack stands. Then remove your wheels, and release the jack the rest of the way. The rear axle should be just hanging there, like this: (Sorry, I did not take pictures during my installation, so you will have to put up with my MS Paint drawing
)
Now, it is time to remove the old shackles. You will want to remove these 2 bolts on each shackle. (Just a side note, that is not the stock shackle, that is the new one. I just didn't take pictures when I put them on)
Now it is simple, Just take out the bolts. These are hard to take out, and will take time. There is no secret for slipping them out, except using a BFH. (Big F***ing hammer)
Once the bolts are taken off, and the old shackles gone, just simply put the new ones there and put the bolts in. Torque the bolts to at least 45ft-lbs.
Now, put the jack under your rear axle, lift it back up, put on your tires, and lift the truck off the jackstands. Now, set it down, and you are done! Just be sure to re-torque your wheels!
My old shackles were rusting out very badly, as you can see here.
What my truck looked like before shackles:
And after shackles installed:
